The present invention relates to an inlet valve assembly that can be integrated in apparatus for dispensing a fluid or a semi-fluid. In general, this type of valve assembly is inserted in a pump body, at the bottom thereof, for performing the function of inlet valve so as to isolate the pump chamber from the tank containing the fluid to be dispensed during the dispensing stage. However, the valve assembly of the invention may also be used as an outlet valve.
A very widely used type of inlet valve assembly uses a metal ball as the dynamic member of the valve, which member comes into sealed contact with a valve seat that is generally an integral part of the pump body under the effect of the pressure exerted on the fluid in the pump chamber. The ball is held in a small space by a valve holder which is in general inserted by force into the bottom of the pump body. The valve holder is provided with a passage that causes the above-mentioned small space to communicate with the pump chamber proper. The ball can be displaced freely within the small space without it being possible for it to close off the communicating passage. It is only during the dispensing stages, i.e. while the fluid is being put under pressure, that the ball is pressed against it seat.
Although widely used in all sorts of dispensing apparatus even other than pumps, such a ball suffers from certain drawbacks.
From the point of view of physics, the ball is made of a material having a high density, namely steel. The weight of the ball is thus relatively large. With respect to its dynamic behavior, when the dispensing apparatus is used upside-down, i.e. with the valve seat uppermost, the ball does not respond immediately to the effect of the pressure, but rather it takes a certain amount of time to reach its place against the valve seat. The pressure must be high enough to overcome the weight of the ball. The difficulty encountered by the ball in moving upwards against its seat is further increased by the fact that its shape is advantageous from the hydraulics point of view. The surface quality of the metal ball and its shape offer very little resistance to the fluid.
Furthermore, from the ecological point of view, the ball constitutes a metal element that prevents the dispensing apparatus in which it is integrated from being recycled, unless it is disassembled first. The current trend is for metal elements not to be included in products that are made of a majority of plastic, as is the case for a pump.
Moreover, while they are being transported or assembled, such balls collide, which damages their surfaces, thereby giving rise to sealing defects.
From the economics point of view, such a ball is a costly part because it is made of steel and it must be exactly spherical. It has also been observed that many such balls are lost during transport or handling because of their spherical shape that is difficult to grasp.
There are other types of inlet valve that do not use balls as dynamic members. For example, some types of dispensing apparatus incorporate a valve in the form of an elastomer washer which is captively mounted in a small space. When the pressure increases in the dispensing chamber of the apparatus, the washer is pressed in sealed manner against the inlet orifice. The sealed contact is achieved merely by the washer being applied axially against the inlet orifice. Thus, to obtain good sealing, it is necessary for the pressure exerted on the washer to be large enough.
In most prior art inlet valves, a valve member (ball, washer, etc.) is confined to a small volume by a valve holder. In all cases, the valve member is not coupled to any other part, and it can float in the volume with which it is associated.
Document WO 95/01226 defines a valve whose valve member has a frustoconical section coming into contact with a frustoconical valve seat. Sealing contact is obtained over an area that is frustoconical because the valve member and the seat define the same solid angle.